Moving journal supplements to repositories?

I would guess this has happened to you: a patron needs a conference abstract or something published in a supplement but it cannot be found, despite your holdings listing it is available. So you try lots of other stuff like Google Scholar or ILL to get it. 

Is there a better way to publish supplements? The Scientist recently published a piece advocating for supplements to be published in repositories instead of journal vendors: The Push to Replace Journal Supplements with Repositories.